Clinical laboratory tests are routinely performed on the serum or plasma of whole blood. In a routine assay, red blood cells are separated from plasma by centrifugation, of red blood cells and various plasma proteins are separated from serum by clotting prior to centrifugation. Hemoglobin, BR and light-scattering substances like lipid particles are typical substances which will interfere with, and affect spectrophotometric and other blood analytical measurements. Such substances are referred to as interferents and their concentrations may be determined by measurement of absorption of different wavelengths of light in serum or plasma specimens which measurements are then compared with values obtained through calibration using reference measurements for the interferent of interest in serum or plasma specimens. BR concentration is determined by measurement of absorption of different wavelengths of light in serum or plasma specimens which are then compared with values obtained through calibration using reference measurements for BR in serum or plasma specimens. On the basis of the results from measurements of one interferent at a time, or any two or more interferents at a time, in comparison with reference measurements of various levels of interferents, a decision is made concerning whether to reject or accept the sample for further testing.
Elevated BR can be due to disease states, hyperlipidemia can be due to disease states and dietary conditions, and hemoglobinemia can be due to disease states and as a result of specimen handling. Clinical laboratories currently emphasize these three potential interferents. Biliverdin, (BV), a fourth potential interferent, is not often mentioned.
Upon visual inspection, BR gives a yellow or orange color to serum and plasma, and is recognized as the major bile pigment in serum or plasma. Specimens which appear greenish in color are usually classified as hyperbilirubinemic, but it is likely that BV is responsible for the greenish color, and these specimens may, nevertheless, have acceptable levels of BR. A yellow color chart is available for visual grading of BR levels in serum or plasma, but there is no known color chart for green bile pigment. Visual inspection may still provide an opportunity for rejection of green specimens, however, for automated systems, no method exists for screening serum or plasma specimens for hyperbiliverdinemia.